enlist vs obligate

enlist

verb
  • To secure; to obtain. 

  • To recruit the aid or membership of others. 

  • To enter on a list; to enroll; to register. 

  • To voluntarily join a cause or organization, especially military service. 

noun
  • One who is enlisted, usually in a military service. 

obligate

verb
  • To bind, compel, constrain, or oblige by a social, legal, or moral tie. 

  • To commit (money, for example) in order to fulfill an obligation. 

  • To cause to be grateful or indebted; to oblige. 

adj
  • Requiring a (specified) way of life, habitat, etc.. 

  • Indispensable; essential; necessary; obligatory; mandatory; unavoidably invoked. 

How often have the words enlist and obligate occurred in a corpus of books? (source: Google Ngram Viewer )